Lua Tutorial by Spectrus

[Lua] tutorial
by Spectrus

Chapter 1: Introduction Hey, I'm Spectrus. This is Lua. Here are some resources.	http://www.studentscomefirst.org/img/external_link.gif
Chapter 2: Variables Dealing with storing, changing, and accessing values.	http://www.studentscomefirst.org/img/external_link.gif
Chapter 3: Tables Branching from variables in to something a little more complex. Storing multiple values within a table and accessing them. Also exploring different possibilities with tables.	http://www.studentscomefirst.org/img/external_link.gif

Chapter 1: Introduction

Hello!

Hello, my name is Spectrus. I'm a staff member here at XenoBot forums. I've written an introductory tutorial to the scripting language Lua. Lua is the scripting language of choice for XenoBot. It can be used to create advanced cavebot scripts with near limitless features (including depositors, refillers, anti-KS). The possibilities with Lua are extensive and I'm going to teach you how to use it. I will apologize in advance, this tutorial is aimed at people who have never looked at any programming or scripting language in their life and are not familiar with the general syntax and format. I will cover it all, and at times it may be boring to those who have prior knowledge. Tough it out, you might still learn something.

Basics

Lua is a scripting language that is designed and maintained by a team from Brazil. It's name, Lua, is the literal word for moon in Portuguese. In fact, it's the name for the moon. Because it's a name, it should be capitalized. Also, it's not an acronym. It should not be spelled LUA. It's correctly spelled Lua. That's one of those minor things that irritates the hardcore enthusiasts.

Moving on from what you can glean from the about section of Lua's homepage, let's discuss why it's important to understand the basics of Lua before jumping in to scripting for XenoBot.

It is completely possible to assemble scripts that do your wishes by simply copying and pasting sections of code that you find around the forums. And while this may be feasible, and acceptable to some, it is my hope that our users will learn to become more self-reliant. By learning the basics of the language in which scripts for XenoBot are written, it will be easy to create anything that you may have a need for without having to ask or search for it.

Resources

• Lua Homepage
• Demo (Good for testing code)
• List of Xenobot functions (Incomplete)

Chapter 2: Variables

What is a variable?

By far, the best analogy of a variable I have seen is that of a box. Let's pretend that a variable is like a box. You can put things in the box, you can see what's in the box, and you can change what's in the box. The same is true for variables. A variable is a storage place to put values. Also similar to a box, it's hard to know what's in it unless it's labelled. Every variable needs a name. So what does this look like in Lua?

lua code:

myVariable = 12

Here, we've created a variable with the name myVariable and given it a value of 12.

I'll talk a lot about good programming practice throughout the tutorial. This is one of those times. Unless explicitly declared, a variable is global. We typically want to work with local variables, not global. We'll discuss what this means when we get in to the topic of scope. Anyways, it is good practice to declare variables like this:

lua code:

local myVariable = 12

This does the same thing as the above example, except we've made the variable local.

Getting back to the analogy of the box, boxes can hold many things. They can hold shoes, they can hold computers, they can hold cups, they can even hold other boxes. Variables, once again, are the same way. They can hold many types of data. Such as... numbers, sentences (known as strings), true/false (known as boolean). Here is an example of each:

lua code:

local myNumber = 12

local myNumber2 = 5.15125617

local myString = "Hello, XenoBot!"

local myBoolean = false

A whole number, a decimal number, a string, and a boolean in that order.

At this point, I'm going to introduce two functions which are a part of Lua. Don't worry, we'll go over functions later. The functions I'm going to introduce are print() and type().

print() is the default method of outputting information. If you want your script to have some sort of text output, you will need to use print() to see it.

type() is important to variables. If you provide it with a variable, it will tell you what kind of variable it is. Meaning it will tell you if it's a number, a string, or anything else.

Here is an example using these functions. What the script would output will be marked by a '>' character at the beginning of the line. With XenoBot, any use of the print() function will result in a green message in game.

lua code:

local myNumber = 12

local myType = type(myNumber)

print(myType)

>number



local myString = "Hello, XenoBot!"

local myType = type(myString)

print(myString)

>string

Displaying what kinds of variables we have using type() and print().

Naming Variables

This is important. It has it's own section, even. A big part of understanding what is happening in a script is coherently named variables. For instance, if I wanted a script that healed at a certain health I could put something like:

lua code:

local a = 100

but then when I try to read through it later, I need to remember what a is for. It would be much better if I did something like this:

lua code:

local hpToHeal = 100

This way, I can clearly understand that whatever value I have put in that variable is intended to be for what hp I want to heal at. Variables can not have any spaces in their name. Thinking of good variable names is important. Also, it's important to make sure that they are readable and as short as possible (without, of course, jeopardizing understanding). Here are some examples of what to do, and what not to do:

lua code:

local variableToRememberHPThatIShouldHealAt = 120

local a = 120

local hEAlthTOheaL = 120

local HEALTHTOHEAL = 120



local healthToHeal = 120

local HpToHeal = 120

local HealAtHP = 120

Variable name examples. Top are not a good idea, bottom are more recommended.

As you may have guessed, the top four are bad examples, and the bottom three are good examples. To learn more about how to form variable names some good conventions are Camel case and Pascal case. Some information can be found here (microsoft.com), but for a more in-depth explanation try googling each one and reading up on it.

Accessing Variables

Alright, we now know how to make variables. The important question is now how do we use them? It's actually quite easy. Once we've made a variable that has a value, we can use it's name in place of the value. What I mean is that if you have a variable called myVariable that has a value of 12, you can then use myVariable in your code instead of writing 12.

lua code:

local myVariable = 12

local anotherVariable = myVariable

Above, we've created the variable myVariable and set it's value to 12. Then, we've created the variable anotherVariable and set it's value to whatever myVariable is. That means that anotherVariable is going to equal 12.

An important note is that a variable must exist in order for you to access it. If you try to access a variable that does not yet exist, you will receive an error. An example of this would be:

lua code:

local myVariable = myOtherVariables

This would result in an error. The variable myOtherVariable has not been created and therefore can not be found.

Now that we have the basics of variables understood, let's move on!

Chapter 3: Tables

What is a table?

A table is a special kind of variable. That's right, I tricked you. You read all that stuff above and thought you had finished with variables once and for all. Well, guess again!

To make a table, you choose a name and instead of just one value, you put multiple values inside curly brackets. Each value needs to be seperated by a comma. In it's simplest form a table looks like this:

lua code:

local myTable={}

print(type(myTable))

>table

Making a table and printing it's type. Note that you can nest functions so you don't need a variable to store the type.

Basically, a table is a bunch of different types of variables all stored under the same name. With tables, you can access each and every part of it as if it was it's own variable. Let's create a table with some values and then access them and print them out.

lua code:

local myTable = {2, "hello!", true, 5.1}

print(myTable[1]) --Prints the first value of your table.

>2

print(mytable[2] -- Prints the second value of your table.

>hello!

print(myTable[3]) --Prints the third value of your table.

>true

print(myTable[4]) --Prints the fourth value of your table

>5.1

Accessing information in a table. Note that anything following the mark "--" is a comment. It is disregarded by the script.

In the same fashion, we can add things to our table.

lua code:

local myTable = {}



myTable[1] = 5

myTable[4] = "Hello, XenoBot!"



print(myTable[1])

>5

print(myTable[4])

>Hello, XenoBot!



print(myTable[2])

>nil --There is nothing in the second spot of myTable.

Creating an empty table then inserting values at specific spots.

Extras

Included with the table variable are some important feature. The first of which is a method of finding how many things are in your table.

Incomplete.

reserved...

reserved....

reserved.....

reserved......

reserved.......

reserved........